Sticking the stalks securely in holes in the rock or between rocks is exactly what I do. That way they can be moved if needed or temporarily removed to frag. Future growth may make the head so heavy that it falls out. Something you are looking forward to I'm sure.
To use
gel super glue remove the frag and squeeze a bb or pea size glob on the spot(s) that will touch the rock. Resubmerge the frag and hold it completely still for 15-30 seconds. Super glue requires h2o to set. Underwater it sets much quicker. It must be "gel" super glue. I buy the 2-packs at any dollar store.
Aloha,
Mark.